This invention relates to a method and apparatus for distributing broadband signals to a subscriber, and more particularly to a system for splitting RF signals and AC power signals originating on the same media, and then distributing these split signals to the home.
When distributing radio frequency (RF) signals, such as video signals, over cable, it is common practice to transmit RF signals and single phase AC power signals over the same coaxial cable simultaneously.
These RF signals originate from a central location commonly referred to as the "headend". The media used to carry the RF signals, typically a coaxial cable, inherently has loss characteristics. Thus an amplifier station must be installed at appropriate locations along the cable to compensate for the losses and deliver the RF signal levels as closely as possible to what they were at the headend. The single phase AC power signal, which in the United States is conventionally 60 Hz, is needed to operate the amplifier stations.
The peak power signals are passed along the cable concurrently with the RF signals. The power level of the AC signal is typically 50,000 times greater than that of the RF signal, and uses different and separate circuitry to operate the amplifier station. Therefore, the AC power signal must be separated from the RF signal at each of the amplifier stations.
Other equipment, in addition to the aforementioned stations, is used in cable distribution for separately distributing RF signals to the home according to subscriber requirements. Certain other equipment such as passives (also referred to as a tap) does not need the single AC power signals for its operation. Passives tap off the RF signal from the cable distribution system and feed the tapped off RF signal to various subscriber equipment. With the advent of interactive television, these passives must also pass RF signals from the home to the headend (upstream) without interfering with AC and RF signals sent to other passives and amplifiers (downstream). The passive equipment, however, must also pass and distribute the AC power signal downstream without interfering with the various operations that relate to the RF signals.
In today's distribution network, certain other equipment such at network interface units (NIU's) and customer interface units (CIU's) are coupled to the home to provide subscriber services to the subscriber such as voice (i.e. telephony), video, data (i.e. modem and facsimile transmissions). The NIU and CIU do need the single AC power signal and a separate RF signals from the passives for its operation. The NIU and CIU because they supply telephony, must supply signals to the home in the event of a power failure. Therefore the NIU and CIU must receive uninteruptable power.
Unfortunately when the prior systems were originally installed there was no provision for providing separate AC power signals from existing passives to the NIU's and CIU's. Thus to upgrade the distribution network to provide this feature the entire passive must be replaced with a new passive that supplies a separate AC power signal to the NIU or CIU. Also when supplying a separate AC power signal to NIU's and CIU's, the current must be limited in the new passive to prevent network failure in the event of a NIU or CIU short circuit. This replacing the passive with one that supplies AC power and adding a current limiting feature increases the cost of upgrading the network.
Subscribers may not need NIU's or CIU's to supply their present demands. Thus it may not be necessary to add current limiting features until the later when the revenues are generated from added services provided by the NIU or CIU. As a result of these market requirements, network operators may want the capability for upgrading their systems but do not want to immediately incur the upgrade cost.
Prior taps distribute RF signals typically carrying video and voice data from a central location, referred to as a headend to a plurality of subscribers. Typically these taps have frequency ranges of zero to 550 MHz. These taps have an input terminal that receives signals from the headend, and an output terminal where these signals received are distributed downstream to other taps. When these taps are upgraded to support higher frequencies, the circuit inside the tap must be removed. Upon removing the tap, service downstream is temporarily disconnected. When supplying video, a short temporary disconnect of service was tolerated by the subscribers. However, taps are now being used to send and receive telephony signals. Thus a temporary disconnection in service is unacceptable.